Record outbreak of West Nile virus waning

Mike Stuart of Dynamic Aviation describes the planeused to spray for West Nile virus in Dallas last month. The last time Dallas used aerial spraying to curb the mosquito population, Lyndon Johnson was in the White House.(Photo: Photo by LM Otero, AP)

This year's outbreak of West Nile is the most serious since the virus was discovered in the United States in 1999, but health officials hope the worst is over.

"We've turned the corner on the epidemic. West Nile virus outbreaks in the United States tend to peak in late August," said Lyle Petersen, director of the Centers for Disease Control and Prevention's Division of Vector-Borne Infectious Diseases.

The mosquito-borne virus causes no symptoms in about 80% of those it infects. The rest develop West Nile fever, with symptoms that can include fever, headache, body aches and sometimes a skin rash. About one in 150 infected people develop the rare but dangerous West Nile neuroinvasive disease, which can cause convulsions, muscle weakness, paralysis and, in some cases, death.

Nationally, cases are up 35% from last week. Texas remained the hot spot, accounting for 50 of the nation's 118 deaths, Petersen said in a telephone briefing. There have been 2,636 cases of of the mosquito-borne disease this year, 1,150 of them -- or 44% -- in Texas.

It's believed that a mild winter and wet spring might have contributed to the high Texas case count, but health officials there still aren't sure, Petersen said.

The next-hardest-hit state, Louisiana, has had 10 deaths and 147 cases.

Two-thirds of the cases have been in six states: South Dakota, Mississippi, Michigan and Oklahoma, in addition to Texas and Louisiana.

The West Nile virus lives in birds. Mosquitoes bite infected birds, become infected themselves, then pass the virus to humans by biting them.

The two worst West Nile virus years previously were 2002, when 284 people died, and 2003, when 264 died, Petersen said. This year is on track to top those numbers. The 2002 outbreak was centered in the East, from Louisiana up through Chicago. The 2003 outbreak was farther west, in the western Plains and mountain states, he said.